Muscle contractionEdexcel A-Level Biology A: Mind map

Exam questions on Muscle contraction

1. A student studies a skeletal muscle under a microscope and measures one sarcomere. When the muscle is relaxed the sarcomere is 2.4 μm long, and each thick filament is 1.6 μm long. When the muscle is contracted the same sarcomere is 1.8 μm long.
   Explain why the H zone becomes narrower when the sarcomere contracts.2 marks
2. Researchers study two isolated skeletal muscle fibres supplied with plenty of ATP. Fibre P is treated with a chemical that prevents calcium ions being released from the sarcoplasmic reticulum. Fibre Q is treated with a chemical that blocks the ATP-binding site of the myosin heads. Both fibres are then stimulated electrically.
   Explain how calcium ions allow myosin heads to bind to actin.2 marks
3. In relaxed skeletal muscle, each myosin head carries ADP and an inorganic phosphate group and is held in a high-energy position. The head is part of a protein that has ATPase activity. Muscle contraction occurs when myosin heads bind to actin and move it, and this cycle needs a supply of ATP.
   Explain the role of ATP and ATPase in the cycle of movement of a myosin head.3 marks